The utilization of miniature ball bearings has enabled pivoting the wheel sets of a movement in cantilever on a sole base plate and thus designing extra-thin movements the thickness of which in their manual winding version does not exceed 1.5 mm. Such a design is described in Pat. No. CH 610 178. In this movement, the barrel is swivelled in the thickness of the movement by its periphery with the help of three rollers, each pivoted on a miniature ball bearing and the ratchet is pivoted on the spindle of the barrel. It has been sought to further reduce the thickness of the movement. Such a reduction is inevitably accompanied by a diminishing of the width of the motor spring housed in the barrel, that is to say, a diminishing of the available energy when the spring is wound, that is to say, a diminishing of the running time reserve of the watch. It is certainly possible to compensate such reduction of energy by using two barrels as is taught in Swiss Pat. No. CH 375 289, but with such small dimensions of the motor spring the significance of friction and energy losses resulting therefrom increases.
Now if one considers the conception of the barrel according to the prior art, it is noted that the barrel is subjected to two opposing twisting moments, one due to the spring and the other to the ratchet. Such twisting moments are not in the same plane, this having inevitably as effect to cause twisting in a plane perpendicular or oblique to the plane of the movement base plate because of the cantilever. The drum of the barrel nevertheless cannot be freely displaced relative to its ideal axis because of the rollers which surround it, this causing friction which is practically impossible to eliminate in such a swivelling arrangement.
The present invention has as purpose to eliminate such friction.